[libvirt] Re: [PATCH 2/3] Introduce monitor 'wait' command
Daniel P. Berrange wrote:
On Wed, Apr 08, 2009 at 09:16:43AM -0500, Anthony Liguori wrote:
> The wait command will pause the monitor the command was issued in until a new
> event becomes available. Events are queued if there isn't a waiter present.
> The wait command completes after a single event is available.
>
> Today, we queue events indefinitely but in the future, I suspect we'll drop
> events that are older than a certain amount of time to avoid infinitely
> allocating memory for long running VMs.
>
> To make use of the new notification mechanism, this patch introduces a
> qemu_notify_event() API. This API takes three parameters: a class which is
> meant to classify the type of event being generated, a name which is meant to
> distinguish which event in the class that has been generated, and a details
> parameters which is meant to allow events to send arbitrary data with a given
> event.
>
Perhaps we should have the ability to turn on/off events, via a 'notify EVENT'
command, and a way turn off the prompt on the channel used for receiving
events.
So if I was interested in RTC change, and VNC client connection events, on
the main monitor command channel we'd do:
(qemu) notify rtc-change
rtc-change notification enabled
(qemu) notify vnc-client
vnc-client notification enabled
(qemu)
So you want to mask out event types? I think you could do this with the
actual wait command either inclusively:
(qemu) wait "rtc-change vnc-client"
...
Or exclusively:
(qemu) wait -x "rtc-change vnc-client"
...
And then in the 2nd monitor channel, a single 'wait' command
would turn
off the monitor prompt and make the channel dedicated for just events,
one per line
(qemu) wait
rtc-change UTC+0100
vnc-client connect 192.46.12.4:9353
vnc-client disconnect 192.46.12.4:9353
vnc-client connect 192.46.12.2:9353
vnc-client disconnect 192.46.12.2:9353
N.B. Right now, wait returns only a single event. This is because the
output format is:
(qemu) wait
1239200822.748241: vm-state: stop
(qemu)
But vm-state doesn't have any details, if it had details it would be:
(qemu) wait
1239200822.748241: vm-state: stop
The virtual machine has stopped.
(qemu)
Since everyone already parses commands like this, I think the format
makes sense. It implies that the event dispatch code has to sit
constantly issuing wait commands.
In my next version of the patch, I expire old events (older than 10
minutes), and also add a -d flag to poll for events vs. wait.
Regards,
Anthony Liguori
Daniel
--
Regards,
Anthony Liguori